Polymers with attached functional groups may be prepared directly by polymerization of functional monomers. Oligomers and polymers prepared by a controlled polymerization processes may have functionality at specific locations along the chain and a specific amount of functionality. For example, functional monomers may be placed periodically along the polymer chain, the initiator may have attached functionality, or the group providing for controlled polymerization may be removed and replaced with a desired functional group. However, there are several controlled polymerization processes and many functional monomers may not be directly copolymerized by every controlled polymerization process. Further, the monomers with desired functionality may not copolymerize in the desired manner using the selected controlled polymerization process. For instance, non-radical based polymerization processes are not as robust as radical polymerization processes, i.e., the polymerization processes are not able to tolerate a wide range of monomer functionality.
Controlled radical polymerization (“CRP”) processes have been described by a number of workers in three ACS Symposium Series edited by Professor Matyjaszewski. [ACS Symp. Ser. Vol. 685, 1998; Vol. 768, 2000; and Vol. 854, 2003.] The use of a CRP for the preparation of an oligo/polymeric material allows control over the molecular weight, molecular weight distribution of the (co)polymer, topology, composition and functionality of a polymeric material. The topology can be controlled allowing the preparation of linear, star, graft or brush copolymers, formation of networks or dendritic or hyperbranched materials and can include such materials grown from any type of solid surface. Composition can be controlled to allow preparation of homopolymers, periodic copolymers, block copolymers, random copolymers, statistical copolymers, gradient copolymers, and graft copolymers. In a gradient copolymer, the gradient of compositional change of one or more comonomers units along a polymer segment can be controlled by controlling the instantaneous concentration of the monomer units in the copolymerization medium, for example. Molecular weight control is provided by a process having a substantially linear growth in molecular weight of the polymer with monomer conversion accompanied by essentially linear semilogarithmic kinetic plots for chain growth, in spite of any occurring terminations. Polymers from controlled polymerization processes typically have molecular weight distributions, characterized by the polydispersity index (“PDI”), of less than or equal to 2. The PDI is defined by the ratio of the weight average molecular weight to the number average molecular weight, Mw/Mn. More preferably in certain applications, polymers produced by controlled polymerization processes have a PDI of less than 1.5, and in certain embodiments, a PDI of less than 1.3 may be achieved.
Further functionality may be placed on the oligo/polymer structure including side-functional groups, end-functional groups providing homo- or hetero-telechelic materials or can comprise site specific functional groups, or multifunctional groups distributed as desired within the structure. The functionality can be dispersed functionality or can comprise functional segments. The composition of the polymer may comprise a wide range of radically (co)polymerizable monomers, thereby allowing the bulk or surface properties of a material to be tailored to the application. Materials prepared by other processes can be incorporated into the final structure as macromonomers, macroinitiators, or as other tele-functional materials or as substrates for CRP processes in either grafting from or grafting to processes. The term tele-functional material includes the materials normally considered to be macromonomers and macroinitiators but is used herein to indicate that other chain end functional materials can now be incorporated into a target structure by consideration of the terminal functionality and target coupling or linking reaction.
Polymerization processes performed under controlled polymerization conditions achieve these properties by consuming the initiator early in the polymerization process and, in at least one embodiment of controlled polymerization, an exchange between an active growing chain and dormant polymer chain that is equivalent to or faster than the propagation of the polymer. A CRP process is a process performed under controlled polymerization conditions with a chain growth process by a radical mechanism, such as, but not limited to; ATRP, stable free radical polymerization (SFRP), specifically, nitroxide mediated polymerization (NMP), reversible addition-fragmentation transfer (RAFT), degenerative transfer (DT), and catalytic chain transfer (CCT) radical systems. A feature of controlled radical polymerizations is the existence of equilibrium between active and dormant species. The exchange between the active and dormant species provides a slow chain growth relative to conventional radical polymerization, all polymer chains grow at the same rate, although overall rate of conversion can be comparable since often many more chains are growing. Typically, the concentration of radicals is maintained low enough to minimize termination reactions. This exchange, under appropriate conditions, also allows the quantitative initiation early in the process necessary for synthesizing polymers with special architecture and functionality. CRP processes may not eliminate the chain-breaking reactions; however, the fraction of chain-breaking reactions is significantly reduced from conventional polymerization processes and may comprise only 1-10% of all chains.
The initiator for a CRP can be a small molecule with additional functionality, an oligo/polymer chain with dispersed or terminal initiating functionality, or initiating functionality can be attached to any physical surface including particles of any composition or size and to flat surfaces. In this manner, functional particles or functional surfaces can be prepared. When only partial coverage of a surface is employed, an array of functional segments on a surface can be formed. Such a material would find utility of many bio-applications where the functional areas could be responsive to different peptides.
ATRP is one of the most successful controlled/“living” radical processes (also CRP) developed and has been thoroughly described in a series of co-assigned U.S. patents and applications, U.S. Pat. Nos. 5,763,548; 5,807,937; 5,789,487; 5,945,491; 6,111,022; 6,121,371; 6,124,411; 6,162,882; 6,407,187; 6,512,060; 6,538,091; 6,541,580; 6,624,262; 6,624,263 6,627,314; 6,759,49 and 6,790,9191 and U.S. patent application Ser. Nos. 09/359,359; 09/534,827; 10/034,908; 10/269,556; 10/289,545; 10/456,324; 10/625,890; 10/638,584; 10/684,137; 10/781,061; 10/788,995; 10/860,807, 10/992,249, and 60/611,853; all of which are herein incorporated by reference, and has been discussed in numerous publications by Matyjaszewski as co-author and reviewed in several publications.
Polymers produced by ATRP methods often contain a terminal halogen atom at the growing chain ends which can be efficiently modified in various end-group transformations, replacing terminal halogens with azides, amines, phosphines and other functionalities via nucleophilic substitution or radical addition and radical combination reactions. Indeed, this transformation chemistry can be conducted on any halogen terminated polymer including polymers prepared by cationic polymerization processes. However, ATRP is one of the most attractive techniques for the synthesis of well-defined end-functionalized polymers.
A group of high-yield chemical reactions were collectively termed “click chemistry” reactions by Sharpless in a review of several small molecule click chemistry reactions. [Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chemie, Inter.l Ed. 2001, 40, 2004-2021] As used herein, a “click chemistry reaction” is a reliable, high-yield, and selective reaction having a thermodynamic driving force of greater than or equal to 20 kcal/mol. Click chemistry reactions may be used for synthesis of molecules comprising heteroatom links. One of the most frequently used click chemistry reactions involves cycloaddition between azides and alkynyl/alkynes to form the linkage comprising a substituted or unsubstituted 1,2,3-triazole. Other click chemistry reactions are chemoselective or regioselective, only occur between alkynyl and azido functionalities with high yield of the 1,4-substituted triazole. Another click chemistry reaction comprises nucleophilic opening of strained ring systems. Typically, the ring opening of strained ring systems comprises three membered ring systems, such as epoxides, aziridines, cyclic sulfates, episulfonium ions, and aziridinium ions. Preferably, epoxides and aziridines are used. The click chemistry reaction is frequently performed in alcohol/water mixtures or in the absence of solvents and the products can be isolated in substantially quantitative yield. See Patton, Gregory C., Development and Applications of Click Chemistry, Nov. 8, 2004.
Selective copper-based click chemistry was described by Sharpless for the preparation of low molecular weight species; [Demko, Z. P.; Sharpless, K. B. Angewandte Chemie, International Edition 2002, 41, 2110-2113-2116] This reaction has been used by Sharpless to conduct a polymerization using two appropriate low molecular weight comonomers (a diazide and a dialkyne). [Punna, S. et. al. Polym. Prep. Div. Polym. Chem. 2004, 45, 778-779.] The resulting polymer had a broad MWD.
Tetrazoles, RCN4R′, belong to a group of five-membered heterocycles, the azoles. Those with no substituent at any of the nitrogen atoms (RCN4H) are acidic, with pKa values similar to carboxylic acids RCO2H (pKa(tetrazole)=4.89, pKa(5-methyltetrazole)=5.56, while pKa(CH3CO2H)=4.751), and are thus sometimes referred to as “tetrazolic acids”. Both classes of compounds dissociated at physiological pH; however, tetrazoles and tetrazolate anions are more lipophilic and more stable towards many metabolytic reactions than the carboxylates. These features make them important compounds for the design of drugs such as antibiotics, antiviral, antiallergic, antihypertensive, and radioprotective agents.
Some polytetrazoles have been prepared by the (co)polymerization of various vinyltetrazole monomers or by the post polymerization reaction of polyacrylonitrile with sodium azide and ammonium chloride. However, such polymers were not prepared using a controlled polymerization process and therefore do not have the properties, such as composition, molecular weight distribution, structure and topology of polymers prepared by controlled polymerization processes.
Traditional procedures for the direct preparation of tetrazoles in polymer backbones have recently been reviewed by Kizhnyaev, [Kizhnyaev, V. N.; Vereshchagin, L. I. Russian Chemical Reviews 2003, 72, 143-164] and described in; DE4211521 where the copolymerization of 2H-tetrazole with vinyl monomers provided homogeneous, reaction-processable polymers which are easily handled during processing. The copolymers, e.g., graft copolymers prepared from acrylonitrile, styrene, polybutadiene, and 5-phenyl-2-(4-vinylphenyl)-2H-tetrazole or 2-methyl-5-(4-vinylphenyl)-2H-tetrazole, are described as being useful alone or in blends [e.g., with poly(butylene terephthalate)] for the preparation of extruded articles showing high-impact strength, high heat deformation temperature, and good chemical resistance.
DE4211522 described that similar polymers, based on vinyl-aromatic monomers, 2H-tetrazoles with vinyl:phenyl substituents, and polydiene graft base are useful in preparation of a polymer membrane, useful for ultrafiltration, dialysis etc.
DE4222953 described the preparation of post-modifiable copolymers by emulsion copolymerization of styrene, acrylonitrile, and 2-methyl-5-(4-vinylphenyl)-2H-tetrazole that are processable by standard thermoplastic methods but could be modified by UV irradiation to provide surface crosslinking for improved impact and tensile strength. I.e., a low level of tetrazole functionality is incorporated by copolymerization and used to initiate a grafting to or a crosslinking reaction.
U.S. Pat. No. 3,397,186 indicated that triaminoguanidinium salts of 5-vinyltetrazole polymers are prepared by copolymerization and are useful as rocket fuel binders.
Stille described copolymerization of vinyl tetrazoles that allowed thermal crosslinking of copolymers containing dipolarophiles and the tetrazoles as nitrile imine dipol precursors. [Stille, J. K.; Gotter, L. D. Kinet. Mech. Polyreactions, Int. Symp. Macromol. Chem., Prepr. 1969, 1, 131-134; Stille, J. K.; Chen, A. T. Macromolecules 1972, 5, 377-384.]
The homopolymer of 2-(4-ethenyl)phenyl-5-phenyl-2H-tetrazole and its copolymers with styrene and acrylonitrile were prepared by Darkow. [Darkow, R.; Hartmann, U.; Tomaschewski, G. Reactive & Functional Polymers 1997, 32, 195-207.] The solution behavior of the tetrazole-containing polymers is dependent on the H-bond participation of tetrazole rings and by hydrophobic interactions between monomer groups. [Annenkov, V. V.; Kruglova, V. Journal of Polymer Science, Part A: Polymer Chemistry 1993, 31, 1903-1906.]
Polymers containing acrylonitrile functionality may be converted to polymers containing tetrazole functionality. U.S. Pat. No. 3,096,312 provides conditions for conversion of polyacrylonitrile to poly(5-vinyltetrazole) with a molecular weight distribution of greater than 2 by heating with NaN3 and NH4Cl in HCONMe2 for 24 hours at 120-5 Degrees.
U.S. Pat. No. 3,350,374 describes the preparation of copolymers of hydroxytetrazoles and hydrazide oximes. These polymers were prepared by modification of another precursor polymer. The polymers are prepared from poly(hydroxamic acids) by treatment with SOCl2, giving poly(hydroxamyl chloride), which was then treated with hydrazine, giving the poly(hydrazide oxime). Treatment with NaNO2 and HCl gives a poly(azide oxime), which then rearranges to poly(hydroxytetrazole). The products are used as ion exchangers and explosives. The process is described as being less dangerous than the polymerization of a vinyltetrazole, but again, the initial polymers were not prepared by a controlled polymerization process and are therefore unable to be tailored to meet the requirements of property selective applications. In all prior publications and discussions on tetrazole-containing polymers, the copolymer had been prepared by standard polymerization processes; therefore, no control over any molecular parameter was possible.
Thus, there is a need for a method of preparing polymers, such as polytetrazole (co)polymers with controlled functionality, topology, and composition.